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Generic AOCS Simulator
2nd ESA Workshop on Astrodynamics Tools and Techniques
ESTEC, September 13-15, 2004
Erwin Mooij
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Introduction (1)
AOCS hardware and software development relies on different simulation environments:
Engineering Simulator
Hard real-time HILT/SILT
No commonality in the development and/or use of these simulation environments:
Internal: differences from project to project
External: prime/sub interfaces
Solution: Generic AOCS simulation environment, to be used in European Space Community
Well documented
Validated models
Generic interfaces, etc.
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MatLab Simulink
EuroSim+ autocode MatLab
SDE + SISSDE +
target board
EuroSim SIL
EuroSim HIL
Control Verification by similarity
EuroSim+ flight code for control
EuroSim EGSE
EM/FM bench
EuroSim EGSE AVTB
MATLAB / SimulinkGAOCS Environment
EuroSimGAOCS Environment
EuroSim / HILT / SILTGAOCS Environment
Objectives:Sub-system Model Development and TestingControl Algorithm Design and TestingEngineering Simulations
Tools:User-friendly GUI for definition and plottingGeneric Dynamics Core and Environmental ModelsLibrary of Sensor and Actuator ModelsUser defined sub-systems can easily be added
Objectives:Real Time Simulationslink to 2D/3D IGS Graphicsadd other coded models
Tools:Use of EuroSim GUI and plotting facilitiesSame Generic Dynamics Core and
Environmental ModelsSame Library of Sensor and Actuator Models
Objectives:ASW validationSCOE backbone
Tools:MIL1553-bus communicationSoftware in loop SimulationsHardware in loop Simulations
life-cycle
Introduction (2)
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Overview
GAOCS Simulator elementsMATLAB/Simulink Environment:
Design philosophy
Physical modelling
Simulator architecture
Functional verification
EuroSim EnvironmentInterface mechanism with MATLAB/Simulink
Real-Time Workshop
ExamplesAdaptive satellite control
Herschel on-board software development
ConeXpress rendezvous and docking
Current status and future work
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MATLAB/Simulink EnvironmentDesign philosophy (1)
Graphical User Interface to learn simulator and for quick access to simulation results
Libraries with Simulink models and corresponding initialisation files
Set-up of simulator with library links
Instantiation of library models, automated initialisation of each instantiation
CMEX functionslocal workspace defined for definition of global variables
Instantiation of simulator core to allow for formation-flying simulator, rendezvous-and-docking simulator, ...
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MATLAB/Simulink EnvironmentDesign philosophy (2)
Facility to plot simulation results
Edit Window: Body Characteristics
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MATLAB/Simulink EnvironmentPhysical modelling
Equations of (translational and rotational) motion for a rigid satellite with up to 4 solar panels, with Earth as central body
Sun and Moon as perturbing third bodies
Tabulated atmosphere according to MSIS-86
Gravitational field according to inverse-square law (+J2, J3 and J4) or GRIM-5C1 (spherical harmonics, n=m=99)
Geomagnetic field based on IGRF-95 (spherical harmonics, n=m=10)
Solar radiation according to inverse-square law
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MATLAB/Simulink EnvironmentSimulator architecture (1)
Main Simulink AOCS simulator window
Generic core
User-defined sub-systems
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MATLAB/Simulink EnvironmentSimulator architecture (2)
Simulink AOCS logic sub-system
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MATLAB/Simulink EnvironmentSimulator architecture (3)
Sensor Library Actuator Library
Main Library Simulink window
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MATLAB/Simulink EnvironmentSimulator architecture (4)
Performance improvement by replacing MATLAB scripts by C-coded S-functions (so-called CMEX S-functions)
Simulator porting to EuroSim: relatively easy due to use of CMEX functions
Use Real-Time Workshop to autogenerate C-code of Simulink simulator structure (per sub-system)
Porting process and integration has been automated to a large extent
Alternative in latest version: integrate Simulink models directly in EuroSim model
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MATLAB/Simulink EnvironmentFunctional verification (1)
Time propagation, both in relative and absolute sense, and frame and co-ordinate transformations
Environment, consisting of the Earth's gravitational and magnetic field, the Earth's atmosphere, the motion of Moon and Sun and the interplanetary environment
Equations of motion, focusing on both translational and rotational motion, and the numerical aspects due to the integration of the differential equations
Perturbations, of gravitational origin, due to third-bodies (Sun and Moon), the Earth-magnetic field, the Solar radiation and the working of the upper atmosphere
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-180 -120 -60 0 60 120 180-90
-45
0
45
90
longitude (deg)
latit
ude
(deg
)MATLAB/Simulink EnvironmentFunctional verification (2)
geostationary transfer orbit
Molniya-type orbit
-180 -120 -60 0 60 120 180-90
-45
0
45
90
longitude (deg)
latit
ude
(deg
)
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EuroSim Environment (1)
Model Editor
Simulation Controller
Application-dependent sub-system models:- generic actuator- AOCS logic- generic sensor
Flight dynamics models:including CMEX functions
Support Library
Datapool:Input/output exchange
Schedule Editor
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EuroSim Environment (2)
EuroSim SILT Architecture
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MRAC application (1)
Design of MRAC for a satellite in a perturbing environment (LEO, solar-radiation pressure and aerodynamic drag)
Tuning of controller parameters in ideal environment, with idealsensors and actuators (MATLAB/Simulink)
corrective control roll channelslew maneuver pitch channelscanning pattern yaw channel
Transfer of models to EuroSim:inclusion of imperfect sensors and actuators, and perturbed environmentstep response on roll angle, stability check
Inclusion of MIL-1553 communication, bus frequency check
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adaptive gain
adaptive gain
adaptive gain
output error
reference state
reference input
user specifications
MRAC application (2)
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generic core
actuator model (error generator)
sensor model (error generator)
MRAC application (3)MRAC system
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MRAC application (4)
Top level Model Reference Adaptive Control System
C-code
includes C-code
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0 5 10 15 20 25 300
0.5
1
1.5
time (sec)
roll
angl
e (d
eg)
0 5 10 15 20 25 30-10
0
10
20
30
time (sec)ro
ll m
omen
t (N
m)
reference model
satellite
satellite
reference model
MRAC application (5)
step-function roll response
XBYB
ZB
c.o.m.
XP,2
YP,2
ZP,1
ZP,2 YP,1
XP,1
Sun
satellite body mass: 1600 kg
solar panel mass: 40 kg
LEO (300x300 km), satellite in full view of Sun
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0 10 20 30 40 50 60 70 80 90 1000
5
10
15
20
25
time (sec)
pitc
h an
gle
(deg
)
0 10 20 30 40 50 60 70 80 90 100-4
-2
0
2
4
time (sec)
pitc
h m
omen
t (N
m)
referencemodel
satellite
satellite
referencemodel
0 50 100 150-1
-0.5
0
0.5
1
time (sec)
yaw
ang
le (
deg)
0 50 100 150-50
-25
0
25
50
time (sec)
yaw
mom
ent (
Nm
)
referencemodel
referencemodel
satellite
satellite
MRAC application (6)
square-wave yaw response
ramp-function pitch response
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MRAC application (7)
0 5 10 15 20 25 300
0.5
1
1.5
time (sec)
roll
angl
e (d
eg)
0 5 10 15 20 25 30-20
0
20
40
60
time (sec)
roll
mom
ent (
Nm
)
satellite
satellite
reference model
reference model
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
time (sec)
roll
angl
e (d
eg)
0 10 20 30 40 50 60 70 80 90 100-0.4
-0.2
0
0.2
0.4
time (sec)
roll-
angl
e er
ror
(deg
)
satellite(MIL 20 Hz)
reference model
MIL 20 Hz MIL 50 Hz
EuroSim SILTEuroSim PSF
100 Hz MIL-bus frequency 50 & 20 Hz
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GAOCS Herschel Implementation (1)
MATLAB / Simulink Environment
Generic Core (Flight Dynamics and Environmental Models)
(External) Sensor Models (3 versions):2 Star tracker models
4 Gyros
2 Quartz rate sensors
Attitude Anomaly Detector
2 Sun Acquisition sensors
(External) Actuator Models (3 versions):RCS
4 Reaction wheels
Controller Models:RCS controller (in-house)
RWS controller (external)
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GAOCS Herschel Implementation (2)
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The Herschel PSF:
EuroSim Environment under LinuxFunctional (PDR) unit modelsModels ported from MATLAB/Simulink using Real Time WorkshopDefining the EuroSim schedule similar to Simulink execution orderVerification against MATLAB/Simulink results:
EuroSim based PSF_V0 Simulator with qualitatively similar resultsCDR unit models integrated, verification against PDR resultsHardware interfaces integratedIntegration of on-board software
GAOCS Herschel Implementation (3)
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ConeXpress R&D simulator (1)
ConeXPress in mated configuration with target satellite
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ConeXpress R&D simulator (2)
Waiting ellipse (relative position chaser-target)
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Current status
Generic simulator for rigid satellites in Earth environment has been designed and implemented in MATLAB/Simulink
Each of the individual models as well as the combination of several models has been evaluated and judged to be correctly implemented
Performance improvement by factor of 20, by using C-coded S-functions
Basis for further development of Generic EuroSim AOCS simulation environment for SIL and HIL testing
(Potential) customers: HERSCHEL, ConeXpres, EarthCare, EXPERT re-entry vehicle, Virtual Satellite, your satellite, ...
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Modelling:Additional satellite shapes, i.e., cone and sphere, which includes the adjustment of the solar-radiation pressure and atmospheric perturbation models
Flexible appendages (NASTRAN data files with mode shapes, etc.)
Addition of tip masses to the appendages
Mass variation due to fuel consumption, including sloshing models
Sun as central body for interplanetary missions
Etc.
EuroSim:Development of GUI, possibly combined with MATLAB/Simulink
SILT/HILT:GAOCS simulator with MIL-1553 communication Herschel
Dedicated (flight) hardware in loop Herschel
Current and future work (1)
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Goal: one AOCS simulation and test environment for European Space Programmes (ESA), possible funding GSTP/TRP/?
Open source of GAOCS Simulator elements
Central management of GAOCS Simulation Environment :Feedback of user models from industry
Screening for potential implementation
Validation of user models and implementation in baseline
Release of next version of GAOCS Simulation Environment
Documentation
Set-up of data interfaces with COTS products (STK, simsat, )
Current and future work (2)